Abstract
Chimeric antigen receptor (CAR) T-cells targeting CD19 mediate potent effects in relapsed/refractory pre-B cell acute lymphoblastic leukemia (B-ALL) but antigen loss is a frequent cause of resistance to CD19-targeted immunotherapy. CD22 is also expressed on most B-ALL and usually retained following CD19 loss. We report results from a phase I trial testing a novel CD22-CAR in twenty-one children and adults, including 17 previously treated with CD19-directed immunotherapy. Dose dependent anti-leukemic activity was observed with complete remission in 73% (11/15) of patients receiving ≥ 1 × 106 CD22-CART cells/kg, including 5/5 patients with CD19dim/neg B-ALL. Median remission duration was 6 months. Relapses were associated with diminished CD22 site density that likely permitted escape from killing by CD22-CART cells. These results are the first to eastablish the clinical activity of a CD22-CAR in pre-B cell ALL, including in leukemia resistant to anti-CD19 immunotherapy, demonstrating comparable potency to CD19-CART at biologically active doses in B-ALL. They also highlight the critical role played by antigen density in regulating CAR function. (Funded by NCI Intramural Research Program)
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